function that_shall_be_run_when_alt_and_c_is_pressed ()
{
...
}

function that_shall_be_run_when_only_c_is_pressed ()
{
...
}
function that_shall_be_run_when_c_is_pressed ()
{
if (key_alt) that_shall_be_run_when_alt_and_c_is_pressed ();
else function that_shall_be_run_when_only_c_is_pressed ();
}

...

on_c = that_shall_be_run_when_c_is_pressed;